In recent years, attention is drawn to an electric powered vehicle incorporating a power storage device (for example, a secondary battery, capacitor and the like) to run using the driving force generated from the electric power stored in the power storage device, as an environment-friendly vehicle. Such an electric powered vehicle includes, for example, an electric car, a hybrid vehicle, a fuel cell vehicle, and the like.
Some of these electric powered vehicles may incorporate a motor generator for generating a driving force to run upon receiving electric power from the power storage device at the time of startup and/or acceleration, and for generating electric power by regenerative braking in a braking mode to store electric energy in the power storage device. In order to control the motor generator according to the running state, the electric powered vehicle is mounted with an inverter.
In order to stably supply electric power required by the inverter and that varies according to the vehicle status, such a vehicle may incorporate a voltage converter between the power storage device and inverter. By using the converter to boost the input voltage of the inverter higher than the output voltage of the power storage device for increasing the power output of the motor and also to lower the motor current than that of the same level output, the size as well as the cost of the inverter and motor can be reduced.
Japanese Patent Laying-Open No. 2006-187186 (Patent Literature 1) discloses an approach of reducing the carrier frequency employed in switching-control of a switching element in a voltage conversion device for a motor drive device when the switching element of the voltage conversion device is affected by the dead time in the region where the voltage command value of the voltage conversion device is in the vicinity of the power supply voltage.
According to this approach, oscillation in the output voltage occurs as a result of not being able to ensure the ON duty that is the essential target due to the dead time in the region where the voltage command value of the voltage conversion device is in the vicinity of the power supply voltage, i.e. the ON duty of the upper arm of the voltage conversion device is in the vicinity of 1.0. The approach allows oscillation in the output voltage of the voltage conversion device to be suppressed.